xu xin wrote: > >> > IP_PMTUDISC_DONT: turn off pmtu detection. > >> > IP_PMTUDISC_OMIT: the same as DONT, but in some scenarios, DF will > >> > be ignored. I did not construct such a scene, presumably when forwarding. > >> > Any way, in this test, is the same as DONT. > > > >My points was not to compare IP_PMTUDISC_OMIT to .._DONT but to .._DO, > >which is what the existing UDP GSO test is setting. > > Yeah, we got your point, but the result was as the patch showed, which hadn't > changed much (patch v2 V.S patch v1), because the fragmentation option of 'patch v1' > used the default PMTU discovery strategy(IP_PMTUDISC_DONT, because the code didn't > setting PMTU explicitly by setsockopt() when use './udpgso_bench_tx -f' ), which is > not much different from the 'patch v2' using IP_PMTUDISC_OMIT. Or IP_PMTUDISC_WANT unless sysctl_ip_no_pmtu_disc is set. But fair point. Explicitly disabling pmtu is not needed. > > > >USO should generate segments that meet MTU rules. The test forces > >the DF bit (IP_PMTUDISC_DO). > > > >UFO instead requires local fragmentation, must enter the path for this > >in ip_output.c. It should fail if IP_PMTUDISC_DO is set: > > > > /* Unless user demanded real pmtu discovery (IP_PMTUDISC_DO), we allow > > * to fragment the frame generated here. No matter, what transforms > > * how transforms change size of the packet, it will come out. > > */ > > skb->ignore_df = ip_sk_ignore_df(sk); > > > > /* DF bit is set when we want to see DF on outgoing frames. > > * If ignore_df is set too, we still allow to fragment this frame > > * locally. */ > > if (inet->pmtudisc == IP_PMTUDISC_DO || > > inet->pmtudisc == IP_PMTUDISC_PROBE || > > (skb->len <= dst_mtu(&rt->dst) && > > ip_dont_fragment(sk, &rt->dst))) > > df = htons(IP_DF); > > > >> > > >> > We have a question, what is the point of this test if it is not compared to > >> > UDP GSO and IP fragmentation. No user or tool will segment in user mode, > > > >Are you saying no process will use UDP_SEGMENT? > > > No, we are saying "user-space payload splitting", in other words, use ./udpgso_bench_tx > without '-f' or '-S'. I see. I guess you heard the arguments why the test does not compare udp segmentation with udp fragmentation: - fragmentation is particularly expensive on the receiver side - fragmentation cannot be offloaded, while segmentation can > Sincerely. > > >The local protocol stack removed UFO in series d9d30adf5677. > >USO can be offloaded to hardware by quite a few devices (NETIF_F_GSO_UDP_L4). > >> > UDP GSO should compare performance with IP fragmentation. > >> > >> I think it is misleading to think the cost of IP fragmentation matters
